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| United States Patent |
6,248,799
|
|
Peretti
, et al.
|
June 19, 2001
|
Material containing expandable microspheres and process for the production
thereof
Abstract
A material for the production by extrusion or molding or calendering of
light articles has a chemical formulation comprising at least a
thermoplastic polymer. A predetermined amount of polymeric microspheres
containing isopentane is added to said at least a thermoplastic polymer. A
process for producing said material comprises a first step during which
the thermoplastic polymer is mixed to further components (such as thermal
stabilizers and/or costabilizers and/or additives) and a second step
during which the mixture is granulated in order to obtain a granular
compound. At the end of the first step, and advantageously immediately
before the beginning of said second step, a predetermined amount of
polymeric microspheres containing isopentane is added to the mixture. Said
material is used for the production by injection molding or extrusion or
calendering of light articles in the shoe industry, particularly of shoe
soles.
| Inventors:
|
Peretti; Giorgio (Verona, IT);
Pasetto; Renzo (Bussolengo, IT)
|
| Assignee:
|
Interplastica S.R.L. (Bussolengo, IT)
|
| Appl. No.:
|
708812 |
| Filed:
|
November 8, 2000 |
Foreign Application Priority Data
| Sep 16, 1997[IT] | VR97A0082 |
| Current U.S. Class: |
521/54; 521/79; 521/81; 521/134; 521/145 |
| Intern'l Class: |
C08J 009/00 |
| Field of Search: |
521/54,79,81,134,145
|
References Cited
U.S. Patent Documents
| 4582756 | Apr., 1986 | Niinuma et al.
| |
| 5272001 | Dec., 1993 | Weisman.
| |
| 5332760 | Jul., 1994 | Weisman.
| |
| 5418257 | May., 1995 | Weisman.
| |
| 5520961 | May., 1996 | Lysell et al.
| |
| 5665785 | Sep., 1997 | McClellan et al.
| |
| 6020387 | Feb., 2000 | Downey et al.
| |
| 6022912 | Feb., 2000 | Spitler et al.
| |
| Foreign Patent Documents |
| 0 513 930 A1 | May., 1992 | EP.
| |
| 1 525 787 | Nov., 1976 | GB.
| |
| WO 95/08590 | Sep., 1994 | WO.
| |
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Oppenheimer, Wolff & Donnelly LLP
Parent Case Text
"This application is a Continuation of application Ser. No. 09/297,233,
filed Apr. 26, 1999, U.S. Pat. No. 6,184,259 which is a 371 of
PCT/IT98/00245 filed Sep. 10, 1998 application(s) are incorporated herein
by reference."
Claims
What is claimed is:
1. A process for manufacturing a material based on polyvinylchloride, said
process comprising:
in a first step, providing a mixed blend of a polyvinylchloride material
with at least one of a thermal stabilizer, a co-stabilizer and a
plasticizer, thereby to obtain a mixture;
in a second step, adding to the mixture a predetermined amount of polymeric
microspheres containing a volatile gas, the second step being carried out
under a strictly controlled thermal condition in order to essentially
avoid both breaking and expansion of said microspheres, and thereby to
create a blended composition;
in a third step, extruding and granulating the blended composition from the
second step, whereby the thermal conditions and the extrusion rate of the
extruder are kept under strict control in order to essentially avoid both
breaking and expansion of said microspheres, said third step resulting in
a granulated material based on polyvinylchloride material containing
microspheres which are essentially integral and unexpanded.
2. A process for the production of a material based on polyvinylchloride,
said process comprising;
a first step wherein polyvinylchloride is mixed with at least one of a
thermal stabilizer, co-stabilizers, and a plasticizer thereby providing a
mixture;
a second step of pouring the mixture from said first step into a multistage
extruder/granulator;
adding a predetermined amount of polymeric microspheres containing a
volatile gas to the mixture inside one of the last stages of said
multistage extruder/granulator, said addition being before effecting
granulation of the mixture, the thermal conditions and the extrusion rate
of the extruder/granulator being kept under strict control in order to
essentially avoid both breaking and expansion of said microspheres, and
wherein said second step results in an extruded granulated blended mixture
of material based on polyvinylchloride containing microspheres which are
essentially integral and unexpanded.
3. A process as claimed in any one of claims 1 or 2, wherein said volatile
gas is isopentane.
4. A process according to any one of claims 1 or 2 wherein said
extruder/granulator is operated at about the lowest temperature
technically suitable for obtaining steady links among the components of
the mixture introduced inside of the extruder, and at rate suitable for
avoiding the breaking of the microspheres.
5. A process as claimed in any one of claims 1 or 2 wherein the temperature
in the extruder/granulator does not exceed about 110.degree. C.
6. A process as claimed in claim 3 wherein the temperature in the
extruder/granulator does not exceed about 110.degree. C.
7. A process as claimed in claim 4 wherein the temperature in the
extruder/granulator does not exceed about 110.degree. C.
8. A process as claimed in any one of claims 1 or 2 wherein the PVC is a
suspension product.
9. A process according to any one of claims 1 or 2, wherein the production
of molded or extruded product has a density value comprised above about
0,2 g/cm.sup.3.
Description
TECHNICAL FIELD
The present invention relates to a synthetic material obtained from a
thermoplastic polymer, said material being advantageously used for the
Production of articles which are provided with good physical and
mechanical properties as well as remarkable lightness.
Besides, the present invention relates to a process for the production of
said material and to the use of the above cited material to produce shoe
components, advantageously soles.
The present invention is particularly applied to the production of light
articles, e.g. articles manufactured by shoe industries, more particularly
to the production of shoe soles.
BACKGROUND ART
The use of foamed polyvinylchloride (in the following PVC) for the
production of many different articles which are obtained, for example, by
means of the screw injection molding technique or by means of a transfert
or intrusion device or by means of an extrusion process is well known in
the art.
Generally, to carry out said techniques a material is used which is based
on foamed PVC, said foamed PVC being combined with suitable additives
which provide the final product with suitable physical and mechanical
properties and which improve its production process.
Among said additives, we can mention, for instance, the plasticizers which
have the specific function to soften the starting polymer; the stabilizers
which prevent occuring of undesired thermal and/or light degradations; the
internal and/or external lubricants which allow the material to be easily
worked.
However, it is also known that the products obtained from a material which
is based on foamed PVC suitably combined with the above cited additives
involve some inconveniences and drawbacks which remarkably limit the use
of said products.
First of all, the articles obtained by a material which is based on a
traditional foamed plasticized PVC as described above are characterized by
a density value which is generally higher than 0,7 g/cm.sup.3, thus said
articles are inevitably rather heavy.
Instead, lightness is a very important feature in the production of many
different articles, e.g. shoe soles as mentioned above.
A further drawback of the articles belonging to the state of the art and
obtained from the above cited material consists in that their external
surface generally shows clearly evident streakings caused by the
generation of consistent amounts of gazeous products produced by the
decomposition of the foaming agent of the starting composition.
It appears to be clear that said streakings are not desirable since they
provide the finished product with a poor aesthetical aspect which is
absolutely unacceptable for particular kinds of products.
In addition to the above cited streakings, which lower the quality of the
article, gazeous bubbles can be formed inside of it. Said Bubbles are
uncontrollably generated during the production process and can also have
remarkable dimensions.
It is evident that said gazeous bubbles are absolutely undesirable since
they can cause swellings and, generally, a decrease of the mechanical
properties of the article as well the lowering of the quality thereof.
A further aspect which is very important in specific applications consists
in that foamed PVC does not provide the finished product with excellent
physical and mechanical properties, e.g. with a satisfactory abrasion
resistance.
Owing to the above cited disadvantages and drawbacks caused by the use of a
material which is based on foamed PVC, it is often preferable to replace
said PVC with other kinds of polymers, e.g. foamed bicomponent
polyurethane.
In fact, although foamed bicomponent polyurethane is more expensive as well
as more difficult to be molded and treated during the production process
than foamed PVC, it allows to produce very light articles having very high
superficial quality.
DESCRIPTION OF THE INVENTION
The present invention aims to obviate the disadvantages and drawbacks which
are typical of the background art, and to provide, thus, for a material
comprising a thermoplastic polymer as main component, said material being
advantageously light and characterized by good physical and mechanical
properties.
This is achieved by means of a material having the features disclosed in
claim 1.
The dependent claims outline particularly advantageous forms of embodiment
of the material according to the invention.
Besides, the present invention concerns a process for the production of a
granular material which is based on a thermoplastic polymer suitable for
being successively molded or extruded to obtain a plurality of articles,
e.g. shoe components.
Said process is carried out by means of the features disclosed in claim 13.
The claims dependent on claim 13 outline particularly advantageous forms of
embodiment of the process according to the invention.
Finally, the present invention concerns the use of a material as disclosed
above for the production of shoe components, particularly soles.
Said use is disclosed in claim 16.
According to an important feature of the present invention, the chemical
formulation of the material which is used to produce light articles
comprises at least a thermoplastic polymer to which polymeric microspheres
containing isopentane are added.
More preferably, the term "thermoplastic polymer" indicates a foamed PVC
resin, but it is evident that any cured rubber can be advantageously used,
e.g. a styrenebutadiene rubber (SBR) or any other thermoplastic polymer.
As cited above, in addition to the thermoplastic polymer of the starting
composition, the material according to the present invention comprises
polymeric microspheres containing isopentane.
Said microspheres act as foaming agent and are added in amounts of some
parts per 100 parts of thermoplastic polymer according to the kind of
thermoplastic polymer which is used and according to the article to be
produced, i.e. according to the features as well as to the physical and
mechanical properties to be provided to said article.
According to a particularly preferred form of embodiment of the invention,
the polymeric coating which is used to obtain said microspheres is metha
acrylonitrile-polymethylmethacrylate, said microspheres being for instance
marketed under the trade name EXPANCEL.RTM..
Said polymeric microspheres containing isopentane are added during the
preparation of the material and, more particularly, at the end of the
mixing stage of the components since it is very important that said
microspheres do not break and do not expand before a predetermined instant
of time.
Successively, when said microspheres expand, i.e. during the molding or the
extrusion stage of the article or during the calendering stage, said
microspheres undergo a structural collapse due to the temperature effect;
however, said structural collapse does not cause the breaking of the
microspheres.
Thus, a changement of the microspheres surface occurs, said surface
becoming sufficiently flexible to allow the expansion of the isopentane
which is contained inside of said microspheres avoiding the gas escaping
from the latter as well as their consequent breaking.
Therefore it is also necessary that the extruder is operated in order not
to break said microspheres, the extruder being placed downstream of a
turbomixer and having the specific function to turn the previously
obtained material into granules.
In the same way, also the successive molding stage, e.g. the injection
molding, to obtain any kind of article has to be operated by taking care
that any adjustment of the principal parameters, e.g. rate, pressure,
temperature, is carried out in order to avoid the breaking of the
polymeric microspheres containing isopentane and to assure their expansion
at a predetermined instant of time.
In the case where a given article is not produced by injection molding, but
it is obtained by extrusion or calendering, it is evident that similar
expedients have to be adopted so as to maintain the integrity and the
expansion of said microspheres.
Since the microspheres are added to the mixture after the mixing of the
other components and, advantageously, immediately before the granulation
stage, it is possible to obtain a granular material inside of which the
microspheres are integer and not expanded; in fact, said expansion will
occur only in the final molding or extrusion or calenderina stage of a
given article, e.g. shoe soles.
In such a way the final article is provided with the physical, chemical and
mechanical properties desired to obtain a light product of high quality.
Besides, the material surface is provided with good aesthetical features so
that, if the material is used to produce shoe soles, even after the
carding stage it shows an integer and smooth surface without imperfections
which are generally due to the breaking of large cells during the
production process.
One or more plasticizers are generally added to the basical formulation of
the material according to the present invention.
In fact, said plasticizers act in such a way as to soften the composition,
thereby providing for remarkable advantages during the production process
as well as conferring specific properties to the final product.
The presence of said plasticizers is important also for determining the
desired mix hardness, said hardness varying according to the ratio
thermoplastic polymer/plasticizer which is used.
This aspect is particularly relevant in the field of producing shoe soles.
Among the plasticizers the use of di-2-ethyl-esil-phthalate (DOP) is
particularly preferred.
Besides, according to the present invention, it is possible to add further
additives to the starting composition inside of the turbomixer in order to
improve the physical and chemical features as well as the mechanical
properties and the workability of said material.
Among said additives we may list, for instance: some thermal stabilizers,
e.g. barium and zinc as well as calcium and zinc as well as barium and
lead; suitable costabilizers, e.g. epoxidate oil of soya; any other
further additives to improve the molding of the material and to increase
its lubrication, e.g. stearic acid.
Thus, the material according to the present invention allows density values
to be reached which are remarkable lower than those typical of similar
materials belonging to the state of the art, said lower values being
comprised in the range from 0,2 to 0,65 g/cm.sup.3, and more
advantageously from 0,4 to 0,5 g/cm.sup.3 ; furthermore, also good
physical and mechanical properties as well as high aesthetical results are
achieved.
A further object of the present invention relates to the use of the
material according to the invention in the shoe industry, specifically in
the production of shoe soles.
Thus, the present invention relates to a specific material, the chemical
formulation of which allows a light article to be produced which is
provided with good physical and mechanical properties as well as with high
quality surface appearance since no disadvantageous and undesirable
streakings or internal bubbles are present as it occurs in articles
produced by means of other formulations known in the art as cited above.
DESCRIPTION OF A FORM OF EMBODIMENT
The material according to the present invention is obtained by means of
devices which are already known in the art and which are used for the
production of thermoplastic materials, e.g. a turbomixer downstream of
which is positioned an extruder provided to turn the mixed material into
granules.
According to an important feature of the invention, the polymeric
microspheres containing isopentane are added to the mixture at the end of
the mixing stage, advantageously immediately before mixture is turned into
granules.
In this way, and taking particular care of the operating parameters of the
extruder-granulator, e.g. the thermal profile of the extruder and the
extrusion rate, a relevant aspect of the present invention is to succeed
in obtaining granules most of which are provided with microspheres which
are still intact and not expanded, said expansion occurring during the
successive molding stage.
According to a further form of embodiment of the process, the polymeric
microspheres containing isopentane are added inside of the
extruder-granulator in correspondence of one of its latest stages.
For example, inside of an extruder-granulator comprising eight or nine
stages, the microspheres are added during one of the latest two or three
stages before the obtainement of the finished material, preferably during
the last stage.
In the following are shown some non-limiting examples of the starting
compositions which can be used to produce the material according to the
invention.
EXAMPLE I
The following is a particular formulation of the material according to the
present invention, advantageously used in shoe industries:
suspended PVC resin 100
plasticizer 65
ESBO 4
stabilizer 4
stearic acid 1
polymeric microspheres containing isopentane 6
wherein said amounts are indicated in parts per 100 parts of resin and
wherein ESBO is epoxidate oil of soya.
EXAMPLE II
The following is a further formulation of the material according to the
present invention:
suspended PVC resin 100
DOP 45
DIBP 15
ESBO 5
stabilizer (Ba--Zn) 5.5
stearin 1
polymeric microspheres containing isopentane 6
wherein said amounts are indicated in parts per 100 parts of resin and
wherein DIBP is di-isobutyl-phthalate.
EXAMPLE III
The following is a further formulation of the material according to the
present invention:
suspended PVC resin 100
DOP 50
DIBP 20
ESBO 5
stabilizer (Ba--Zn) 5.5
stearin 1
polymeric microspheres containing isopentane 5
AZDC 0.3
wherein said amounts are indicated in parts per 100 parts of resin and
wherein AZDO is azodicarboamide, generally used as foamed agent.
EXAMPLE IV
The following is a further formulation of the material according to the
present invention:
suspended PVC resin 100
DOP 20
DIBP 15
ESBO 5
stabilizer (Ca--Zn) 5.5
stearin 1
polymeric microspheres containing isopentane 5
AZDC 0.3
wherein said amounts are indicated in parts per 100 parts of resin.
EXAMPLE V
The following is a further formulation of the material according to the
present invention:
Europrene Solt 177 130
Calprene 485 125
paraffinic oil 45
polymeric microspheres containing isopentane 12
AZDC 0.4
zinc of stearate 0.3
wherein, in this case, instead of the traditional PVC resin, a
thermoplastic rubber (Europrene Solt 177+ Calprene 435) is used.
As cited above, in order to achieve the aim of the present invention it is
necessary that the polymeric microspheres containing isopentane, which
have to, be added during the production of the material and more
specifically at the end of the mixing cycle, do not break and do not
expand before a predetermined time.
Therefore, it is necessary to carefully operate the extruder which is
downstream of the mixing stage in order to obtain a granular material
inside of which the microspheres are and have to be maintained integer and
not expanded till the suitable molding or extrusion or calendering time of
the finished article.
This means that, according to the present invention, it is very important
that the operating parameters of the extruder-granulator, e.g. the thermal
profile of the extruder and the extrusion rate, have to be maintained
under control and inside of suitable ranges in order to obtain granules
the most of which are provided with microspheres still intact and not
expanded, said expansion occurring during the successive molding or
extrusion stage of the finished article.
According to a particular form of embodiment of the present invention, the
extruder-granulator is operated at the lowest temperature which is
technically allowed to realize a steady link among the components of the
mixture introduced inside of said extruder-granulator, and at the most
suitable rate for avoiding the breaking of the microspheres.
Table I, represented in the form of a comparative table, shows a working
example of an extruder which is positioned downstream of the mixing stage;
in said example the temperature inside of the different zones of the
extruder (indicated with numbers from 1 to 9) and the rate of the worm of
said extruder are considered as the principal working parameters of the
extruder.
Furthermore, the presence of the filter, which is positioned at the end of
the extruder-granulator, has been considered as a further process
parameter.
Said example compares the temperature and rate values of the extruder when
a traditional formulation of PVC is used and when a material according to
the present invention is used, the thermoplastic polymer of said material
being PVC.
TABLE I
WORKING PARAMETERS OF THE EXTRUDER
Material according
Traditional formulation to the invention based
with PVC on PVC
ZONE 1 140.degree. C. 80.degree. C.
ZONE 2 150.degree. C. 90.degree. C.
ZONE 3 160.degree. C. 100.degree. C.
ZONE 4 160.degree. C. 110.degree. C.
ZONE 5 155.degree. C. 105.degree. C.
ZONE 6 150.degree. C. 100.degree. C.
ZONE 7 145.degree. C. 95.degree. C.
ZONE 8 140.degree. C. 90.degree. C.
ZONE 9 135.degree. C. 85.degree. C.
Worm rounds 30 rpm 18 rpm
Filter present not present
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